Observations on the Microanatomy ofCoccolithus PelagicusandCricosphaera Carterae, With Special Reference to the Origin and Nature of Coccoliths and Scales

Abstract

Coccolith structure, mode of origin and arrangement on the cell surface have been investigated in two marine coccolithophorids, Coccolithus pelagicus (Wall.) Schiller and Cricosphaera carterae (Braarud et Fagerland) Braarud, by means of light microscopy and electron microscopy of whole mounts and sections. The presence of flagellar bases in Coccolithus pelagicus is also demonstrated in spite of the fact that the cells of this phase of the life-history are non-motile. In both organisms the coccoliths are shown to be accompanied by unmineralized scales, details of which are illustrated; in particular, each coccolith is attached to the margin of an unmineralized oval plate which completely covers the central ‘pore’ on the side towards the subtending cell. Scales and coccoliths arise within the cisternae of the single Golgi body in a manner closely resembling the origin of scales in species of Chrysochromulina. It is therefore suggested that the coccoliths of the two taxa investigated can be interpreted as modified (and calcined) scale rims.

Coccolith biomineralisation studied with atomic force microscopy

“…3); we suggest that the base-plate is located between the two. Our SEM observations suggest that this is also the case for species of Umbilicosphaera, although TEM (transmission electron microscopy) studies of them have indicated that the base-plate underlies the coccoliths (Manton and Leedale 1969;Inouye and Pienaar 1984). This suggests that TEM microtome observations of coccolith-scale relationship need to be assessed carefully, given the problems of coccolith disruption and dissolution during cytological preparation.…”

“…Rather remarkably, this scale does not underlie the coccolith, as predicted by e.g. Manton and Leedale (1969), but lies part way up the central tube and appears to pass into the cocccolith. Elliptical scales approximately 2 mm across, displaying a micro®brillar structure of concentric ellipses and radially projecting lines, are often observed on the proximal surface (Pl.…”

“…Morphogenesis of biominerals grown in vesicles is thought to result from two types of in¯uence: cellular stresses that can direct vesicle shape and the action of functional organic molecules that inhibit or accelerate growth (Mann 1983(Mann , 1993. Both mechanisms modify patterns of growth so that the morphology of the resulting biomineral is very different from that of its inorganically grown counterpart.…”

“…It results in both amorphous and crystalline materials, with oxides, silica and carbonates being common. The control exerted by the organism ranges across a spectrum from biologically induced biomineralisation, where precipitation occurs extracellularly as a by-product of the metabolic activity of the organism, to biologically controlled mineralisation, where composition, crystallographic structure and morphology is completely regulated (Mann 1983). End products of biologically controlled biomineralisation reach a strength,¯exibility and complexity that is far superior to materials that can be manufactured in the laboratory (Mann 1993).…”

“…1, ®gs 1±2) (Young 1993). It has an organic base-plate, which is patternless except for a slight thickening at the margin, and small oval scales with radial and concentric ®brils (Manton and Leedale, 1969;Billard 1994). The bar is the only part of the coccoliths that is not formed by the V and R elements of the proto-coccolith ring.…”